Composite flexible moistureproof wrapping tape or sheet



COMPOSI'E FLEXIBLE MOISTUREPROOF WRAPPING TAPE OR SHEET Filed Feb. 10,1943 July 6, 1948. c F. l-lEssELRoTl-l 2,444,443

` M55 oFF/ases nvezvor arneys Patented July 6, 1948 COMPOSITE FLEXIBLEMOISTUREPROOF WRAPPING TAPE OR SHEET Charles Francis Hesselroth, LosAngeles, Calif.,

assignor to Minnesota, Mining & Manufacturing Company, Saint Paul,Minn., a corporation of Delaware Application February 10, 1943, SerialNo. 475,374

2 Claims.

My invention relates to the production of waterproof and moisture vaporresistant, flexible, protective Wrapping material, especially a wrappingsheet having the characteristic of being self-sealing. The wrappingmaterial may be in sheet or tape form.

Waxes, whether vegetable, animal, or mineral, have of course long beenused as waterproofing agents for one purpose or another. Wax films ofthemselves, as heretofore known, have been fragile and hard to handle,and the films were therefore commonly applied to the surfaces of carrierwebs such as paper or cloth, in order to provide for the handling andsupport thereof. In pursuit of a wrapping material of improved type ascompared lwith ordinary surface-coated wax paper, and the like, variouscombinations of webs were used, the combination being eiected by the useof various adhesives and by the waxes themselves. Thus a glassine sheethas been attached to a paper sheet by means of Wax; Cellophane has beensimilarly combined with paper. However such composite constructionsleave much to be desired, particularly for uses as hereinafterdiscussed.

The most widely used waxes have been of petroleum origin. Parain, acrystalline wax, represents one type. Amorphous wax, viz. amicrocrystalline type of greatly improved ductility, has also beenemployed in some constructions, e. g., as a thin center layer betweenunwaxed sheets of papers, and when compounded with other materials, as asurface coating on paper.

Even an unbroken -lm of wax will allow the passage of moisture vapor, ata rate dependent on the type of wax or wax mixture, the difference inrelative humidity on opposite sides of the film, the temperature, andthe thickness of the film. Microcrystalline Wax shows less moisturevapor transmission than does ordinary paraffin wax, i. e. the ordinarycrystalline type of wax. Further, the microcrystalline product is muchless susceptible to breakage, as by creasing or folding or shattering ofa thin film, whether by itself or supported on a carrier web. However,when coated or rolled out in a thin film in practice, y or when appliedto a carrier web, particularly.

mission. Films of glassine or Cellophane applied to such a layer or lm,so longas the resulting laminated sheet remains integral, aid inretarding the penetration cf water or moisture, :but are themselveshydrophilic and susceptible to the action of moisture to a considerabledegree;

hence they do not prevent moisture transmission therethrough, but onlyretard it for a time. A further drawback of such materials as glasslneand Cellophane is that, if water contacts them while in use in suchlaminated sheet structures, the wax films or coatings tend to peel offof the same, i. e. the composite sheet delaminates. This may bedemonstrated by forming a wax film on one surface of a Cellophane sheet,then placing the composite sheet in Water; the wax lm, which at firstwas firmly adherent to the cellophane, may after a few moments soakingbe removed with ease.

Surface coating, and even partial impregnation, of paper leaves anuntreated area at the center of the web through which water or moisturevapor may readily pass and into which it may penetrate. The cellulosicfibers of that area, being free or relatively free of wax, are swelledand weakened by the moisture reaching them. After prolonged exposure toconditions of high humidity or to contact with liquid water, the web'will therefore have permitted the passage of considerable moisture andwill also have an increased tendency toward delamination or splittingwithin the fibrous sheet. Swelling tends to break sealed joints and isotherwise deleterious. These defects are also progressive, i. e. tend toaggravate themselves.

In using moisture-resistant wrapping material of this invention for theprotection of metal orother objects, e. g. gun barrels, motor parts,etc., which may be shipped long distan-ces or stored for long periods oftime, the web is sometimes formed into a box or bag or other type ofcontainer, the edgesv of which may be sealed simply by folding andpressure, and, where desired, 'by the application of an additionalcoating of wax, the final closure being made similarly. For method oftenfound to be more convenient and advantageous, and for which my wrappingsheet material in its preferred form is suitable, is the application ofthe wrapper in strip or tape form. Various wrapper sheet materialsavailable in the past did not lend themselves to this usage, e. g.because of the dlfliculty of obtaining an effective smooth coverage ofthe article and sealing of the edges of the wrapping. My wrappingmaterial overcomes this difficulty, among others, as rwill be seen fromthe description as a whole,

It is therefore an object of the present invention Ito provide aflexible waterproof and moistureproof wrapping material in tape or sheetform. A further object is to provide a waterproof and moisture vaporresistant sheet comprising a film of ductile wax reinforced by a fibrousmaterial or base. Another object is to provide a reinforced film orsheet of ductile wax or equivalent Which is laminated to, and covered onat irregularly shaped articles, however, a

least one surface thereof by, a continuous film of substantiallynon-porous and moisture-resistant material, e. g. cellulose acetate. Afurther object is to `provide a flexible, waterproof and moistureproof,wrapping material in tape or sheet form which is self-sealing. A stillfurther object is to provide such a. wrapping sheet material, i. e. ofself-sealing character, in the form of rolls which may be readilyunwound when desired. These and other objects-and advantages will beunderstood from the description as a whole.

For the sake of a quick understanding of illustrative embodiments ofconstructions of the present invention, and of portions of suchconstructions, reference is made to the accompanying drawing, in which:

Figure 1 represents a film of amorphous adhesive wax l I reinforced andsupported by a web of fibers I2, the surfaces 2I of the film being freeof fibers and relatively smooth.

In Figure 2, the web composed of fibers I2 embedded in the wax layer isin the form of a creped or embossed sheet, so that the wax surfaces 22and 23 are uneven and wavy.

In Figure 3, a thin continuous film of moistureresistant material I3,previously coated on both sides with wax, has Abeen applied to surface22 to form an intermediate continuous smooth wax phase 24 and to leave asmooth externalsurface 2| of wax II on the composite sheet.

For the sake -of clarity in illustrating the invention the thickness ofmy wrapping sheet has been greatly exaggerated in the drawing, as willbe obvious.

For producing the films of this invention, a microcrystalline oramorphous wax, for example one having a melting point of approximately155 F. as determined by A. S. T. M. method D-127, or an equivalentmaterial, may be used. Since the presence of water or high humidity isgenerally conducive to the growth of organisms such as molds, it isdesirable to include in the wax a mold inhibitor, such as pentachlorphenol, for example 0.1% based on the weight of the wax. In some casesit is desirable to control the acidity of the final product; this may bedone by adding sufcient alkaline material, for example triethanolamine,so that the pH of a water extract of the final product will be withinthe limits desired. For example, addition of about 0.03% oftrlethanolamine has been sufi'icient with some lots of material to givea final pH valueof 6.5-7.5. These materials are conveniently added tovthe i melted wax before the formation of the final film.

They may of course be omitted where their presence is unnecessary. y f

As 1a convenient method of producing the reinforced wax films of thisinvention, a pre-formed web of fibrous material is pre-heated to removeexcess moisture, is dwrawjim thro uglfi` a VA bathfof meltedcompoundedwax, is passed between rolls` orba'rst control the weight ofwax, and is then cooled, either by air or by water. Any or all of theaforementioned steps may be varied, modified, deleted in part orreplaced by others, according to procedures well understood in this art;forexample, note the disclosures of the patents hereinafter designated.However, various other procedures well known in the earlier prior artmay also be used. The temperature of the wax should be so adjusted as toprovide complete saturation of the fibrous web during its passagethrough the bath, and, at the same time, to maintain a suiciently highviscosity so that an effectively thick film will be obtained. For thewax as described in the preceding paragraph, a temperature of 16S-175 F.has lbeen found suitable and advantageous. The final lm of a commonembodiment hereof will weigh in the neighborhood of 50-60 grains per 24square inches, of which the wax will vconstitute about 35-50 grains, theremaining Weight being mainly the embedded fibrous `or reinforcingmaterial. i

For the furtherlprotected lm of Figure 3, the fiber-reinforced wax filmis prepared as before. Simultaneously, a film of moisture-resistant and,preferably, relatively hydrophobic character, such as a suitablyplasticized cellulose acetate film, is passed through the same or anequivalent bath of melted compounded wax, and is then placed in contactwith one face of the first film by passing the two together between theweightcontrolling rolls or bars. The composite film is then cooled,which should'be done as soon as possible after the combination has beeneffected in order to chill the wax below the temperature `at which itsinternal strength would be insuiiir cient to prevent delamination of thecomposite.

The pre-formed fibrous web is preferably of aI soft, porous, flexiblenature, and may be formed in any of the usual ways, as by depositionfrom suspension, carding, or even weaving. It may be in a flat or smoothstate, or may be "wrinkled, creped, or otherwise mildly corrugated. Thefibers may consist of cellulose fibers, especially alpha cellulosefibers as obtained from wood; but

they may also be composed of such relatively hydrophobic fibers as-those of cellulose derivatives such as cellulose acetate; glass fibersor various of the synthetic fibers of resinous or other nature may alsobe used. A preferred form of fibrous web is typified by the absorbentcrepe paper known as white Walpole crepe, weighing 35 lbs. per ream of480 sheets 24 in. x 36 in.

For the additional film of Figure 3, a film is selected which ismoisture-resistant, flexible, and possesses a surface to which the waxfilm will exhibit sufiicient adhesion. Cellulose acetate, celluloseacetobutyrate, Pliofllm (rubber hydrochloride), etc., are examples ofsuch films. Cellulose acetate film is a preferred material.

While the flat-,surfaces 2| of Figures 1 and 3 are effective anddesirable for some purposes,

there is additional advantage to be gained in having at least onesurface wavy and irregular as at 23. When the product of Figure 3 iswound up into roll form, or laid in a stack as individual sheets, withdue precautions being taken to avoid 'I the application of unnecessarypressure to such roll or stack, the waviness of surface 23 is effectivein preventing complete contact vwith surface 2|, and the roll or stackis thus more easily unwound or unpiled. But due to the soft nature ofthe fibrous web and the ductility and adhesiveness of the wax, increasedpressure, such as is applied to the edges during the covering of apackage with'this flexible wrapping material, is sufficient to establishan effective bond.

An illustrative embodiment of my preferred material constructed inaccordance with the above disclosures is therefore composed ofmoldresistant and substantially neutral amorphous, microcrystalline Waxhaving white Walpole 35 lb. crepe paper embedded therein, and No. 88cellulose acetate film laminated thereto with a film of wax, with a thinexposed wax coating on the other surface of said acetate film. Such acomposite sheet will have a total weight of 68-70 grains per 24 squareinches, of which at least 47 grainsV Will be wax. It will have anoverall thickness of approximately fteen thousandths of an inch, and amoisture permeability value of as low as 7 grains per square meter per24 hours, measured at 120 F. with a 100% relative humidity differential,i. e. 100% relative humidity on one side of the wrapping sheet andapproximately zero humidity on the other side thereof. 'I'he material isalso resistant to the passage of grease or oils. Opposing surfaces ofthis sheet may be easily sealed together at ordinary room temperaturesby moderate pressure, as with the fingers; yet the seal may be readilybroken when desired, e. g. for inspection. The sheet is ilexible and mayeasily be made to conform to irregular shapes and objects. It is alsorelatively translucent,'which permits identification or rough inspectionof the contents Without unsealing. Bending or folding of the sheetproduces some disruption of the wax film when carried to extremes, andcauses Whitening and opacity; but does not break the acetate lm. If thislastmentioned condition arises, my wrapping sheet material continues togive an extent of protection much superior to that of prior art wrappingsheets under such a condition.

The waterproofness of the edge bond between surfaces 2| and 23 of Figure3, for example, orv

even between flat surfaces, may be further improved by the applicationof additional quantities of the Wax to one or both of the contactingsurfaces prior to their being pressed together. The wax may be appliedhot by means of a brush. If desired, an article so wrapped may beunwrapped for inspection merely by breaking the wax bond, and may thenbe re-wrapped and re-sealed by again pressing the waxed surfacestogether and without the application of any further coating of Wax orother adhesive.

Materials such as Cellophane sheets or glassine paper sheets are not theequivalent of the cellulose acetate or like sheets or films in mycombination, for reasons already indicated hereinabove. In compositesheets including one or more wax layers or films and a sheet ofCellophane, glassine, parchment or the like, if the Cellophane orglassine paper, etc., becomes Wetter with water at a cut edge, the sameloses its bond to the wax and as a result the composite sheet starts todelaminate; and, when delamination once begins, deterioration of thecomposite sheet by further delamination, etc., is quite rapid uponfurther contact with water and various other materials.

Heretofore, in an attempt to secure greaseproofness in :food packages,and to resist loss of Water from the foods, Cellophane, glassine and thelike have been laminated to sheets of paper having a surface coating ofwax, or which are impregnated somewhat with Wax. For example,

note generally Wilshire U. S. Patent No. 2,123,760 60 wrapping sheet,particularly in the respects just indicated. The use of a hydrophilicsheet such as Cellophane or glassinepaper was fairly satisfactory forcertain uses in providing the single l" quality of greaseproofness, butcomposite struc-70 Number tures comprising such sheet materials hadalre-f stricted utility and, for many uses, a. rather limiteddurability. as will be seen from the above.

By the use of a sheet material such as the acetate lm herein described,particularly when employed in combination with a reinforced lm or layerof amorphous wax, beeswax or the like,

5 or combinations containing the same, I have been able to produce awrapping tape or sheet ma terial which is thin, flexible and serviceableand, at the same time, one which is highly moistureresistant, resistsdelamination and, incidentally,v is also greaseproof. However thequality of Vgreaseproofness is not sov important as highmoisture-proofness and durability where my Wrapping sheet is employed toprotect metal parts against rusting, corroding, etc., during longperiods of shipment and/or storage. In addition to obviating the defectsof Cellophane, etc., of prior constructions by the employment of therelatively hydrophobic acetate film, or the like, as hereinabovedescribed, I also have found I can secure a strong bond between. theacetate film and the reinforced wax lm and can thus secure an integraltough and mechanically 'streng composite wrapping sheet, which also `hasthe other virtues above set forth.

While my invention has been described and illustrated by specificexamples and description, it will be understood that all embodiments andvariations within the scope of this specification and the appendedclaims are contemplated.

What I claim is:

1. A flexible Water and moisture vapor resistant sheet material' of theclass described comprising a film of microcrystalline amorphous waxsupported and reinforced by a porous` fibrous web which is completelyand continuo`s'ly impregnated and covered by the wax throughout, theweight of thewax bei-ng at least twice the weight of the fibrous Web,the said sheet material being free of any continuous lm of a hydrophilicmaterial in the interior thereof, 'its two surfaces being fiber-free andmutually adherent when pressed together under moderate pressure and itswater and moisture vapor resistance being substantially equal in alldirections within the sheet throughout its extent.

2. A laminated sheet material comprising' thel material of claim 1adhered by the Wax to a con-l REFERENCES CITED The following referencesare of record in the le of this patent:

UNITED STATES PATENTS Name Date Miller et al. Apr. 27, Schwarwath 1 May14, Rayner May 21,V Kirschbraun June 24, Angier Oct. 18, Angier Dec. 18,Charch Apr. 16, Hunt et al. Dec. 14, Shoan Aug. 4,

FOREIGN PATENTS Country Date Great Britain May 5, 1936 Number 340,810674,219 1,714,240 l1,765,839 ,.f`1,882,715 '1,984,910 1,997,8572,102,207 l 2,291,838

